This invention relates to a cannula used for vessel retraction, and more particularly to a cannula and method for performing both vessel dissection and transection.
One important component of a surgical cannula is the tip, disposed on the distal end of the cannula. A properly configured tip can provide important functionality to a cannula. For example, the functions of vessel dissection and transection are commonly performed by two separate instruments. The device described in the pending application Ser. No. 08/907,691, entitled xe2x80x9cTissue Separation Cannula with Dissection Probe and Method,xe2x80x9d filed on Aug. 8, 1997 now U.S. Pat. No. 5,980,549, discloses a device for separating surrounding connective tissue from a vessel (dissection). The device described in the pending application Ser. No. 09/102,723, entitled Vessel Isolating Retractor Cannula and Methodxe2x80x9d, filed on Jun. 22, 1998, discloses a device for retracting the vessel, ligating side branches, and transecting the branches to allow removal of the vessel. It is desirable to use a single device for performing the above functions.
The construction of a cannula tip also affects the visual field provided to a surgeon through an endoscope. When an endoscope is situated in a lumen of the cannula, the surgeon looks through the endoscope and through the transparent tip to view the surgical site. It is desirable to have a tip which maximizes the visual field of the endoscope.
The cannula tip may also be used to dilate a tunnel or anatomical space through tissue planes. In pending application Ser. No. 09/133,136, now abandoned entitled xe2x80x9cTISSUE DISSECTOR APPARATUS AND METHOD,xe2x80x9d filed Aug. 12, 1998, assigned to the same assignee as the present application, and which is hereby incorporated by reference, a cannula is constructed with a bulbous element near the tip of the cannula for performing tissue dilation as the cannula is advanced. Cannula tips for dilating tunnels through tissue require force in order to advance the cannula and dilate the tissue. It is desirable to have a tip which can perform tissue dilation or dissection using a minimal amount of force and causing minimal trauma.
In accordance with the present invention, a tissue retractor is positioned within a cannula with a dissection cradle end of the retractor positioned at the distal end of the cannula. The retractor includes a first portion that has an axis approximately parallel to a central axis of the cannula, and a second portion that has an axis which is at an angle with respect to the central axis of the cannula. The dissection cradle is located at the distal end of the second portion of the retractor. In another embodiment, the retractor includes two legs having substantially parallel axes that selectively protrude from the distal end of the cannula. The protruding legs support the dissection cradle formed in the shape of a loop that is positioned in a plane skewed relative to the axes of the legs, with a bottom of the loop directed away from the cannula. Thus, in operation, when the surgeon locates a vein and side branch of interest, the surgeon extends the retractor to cradle the vein in the dissection cradle. Once cradled, the retractor may be fully extended to urge the vein away from the axis of the cannula, causing the side branch to be isolated and exposed to a surgical tool. The surgical tool may then be extended from within the cannula to operate on the isolated and exposed side branch.
In another embodiment, the top of the loop of the dissection cradle is flat and thin, allowing atraumatic support of the vein, and minimizing contact between the retractor and the surgical tool. In yet a further embodiment, the retractor includes a single leg with the loop formed by the one leg of the retractor, and with a stopper coupled to the distal end of the retractor. In still another embodiment, the cannula comprises a sliding tube which encases the retractor, and in a first position is extended out to encase the second portion of the retractor, and in a second position is extended to encase only the first portion of the retractor. In response to the sliding tube being in the first position, the second and first portions of the retractor are both approximately parallel to the axis of the cannula. In response to the sliding tube being in the second position, the second portion of the retractor is skewed relative to the axis of the cannula.
In accordance with an alternate embodiment of the present invention, a removable, transparent tip is positioned at the distal end of the cannula to provide a single cannula for performing dissection and transection. When attached, the tip seals the distal end of the cannula in a fluid resistant manner. The tip is conical and ends in a sharp interior point and a slightly rounded exterior point which allows the surgeon to bluntly dissect tissue in the area of interest under endoscopic visualization. When tissue dissection is complete, the surgeon can remove the tip from the cannula, and the surgeon is now able to use the cannula to transect side branches and vessel ends. In order to maximize the visual field provided by the endoscope, the tip is configured to allow the apex of the tip to be aligned with the central axis of the endoscope. In one embodiment, a distal end of the tip is tilted in an oblique fashion to allow the apex of the tip to align with or near to the central axis of the endoscope. In an alternate embodiment, the conical end of the tip has unequal taper angles relative to a plane of transition between the cylindrical and conical portions of the tip, thus skewing the position of the apex of the tip into alignment with or near to the central axis of the endoscope.
In another embodiment, wing-like protrusions are provided about the cannula near the tip to dilate tissue surrounding the vessel of interest. In one embodiment, the wing-like protrusions are diametrically aligned in a planar configuration with tapered forward edges extending rearward from near the apex of the tip. The planar configuration of the wing-like dilating protrusions near the tip substantially reduces the resistive force encountered during advancement of the cannula through tissue. The wing-like protrusions are positioned on opposite sides of the tip to dissect tissue to form a cavity that may attain a round cross-section under insufflation, thus providing the same resultant tissue dilation as provided by a solid oval dilator, but with less force required to accomplish the tissue dilation. In an alternate embodiment, the leading edges of the wing-like protrusions are curved in a parabolic configuration away from the distal end of the cannula to provide the necessary dilation.